1. Field of the Invention
The present invention relates to a chloroprene rubber and a chloroprene rubber composition. More specifically, it relates to a chloroprene rubber and a chloroprene rubber composition to be molded in mold.
2. Description of the Related Art
Chloroprene rubbers, which are superior in heat resistance, weather resistance, ozone resistance, and chemical resistance, have been used in various fields such as of general industrial rubber products, automobile parts, and adhesive agents. Such chloroprene rubber molded articles are produced generally by molding a chloroprene rubber composition containing chloroprene rubber and additionally vulcanizing agents, vulcanization accelerators, fillers, and others into a particular shape and vulcanizing the molded article (see, for example, Patent Document 1).
On the other hand, chloroprene rubbers have a problem that, when chloroprene rubber molded articles are produced by a method of using a mold, such as injection molding, extrusion molding, or press molding, the resin blend easily remains deposited or layered on the internal surface of the mold. Such mold staining leads to deterioration in dimensional accuracy and appearance and thus in quality of the molded article.
Chloroprene compositions containing a component that is effective in preventing the mold staining were proposed (see, for example, Patent Documents 2 and 3). Specifically, Patent Document 2 discloses a chloroprene rubber composition comprising 100 parts by mass of a chloroprene rubber and 1 to 10 parts by mass of a polyethylene glycol having an average molecular weight of 8000 to 11000. Alternatively, Patent Document 3 discloses a chloroprene rubber composition comprising 100 parts by mass of a chloroprene rubber and 1 to 50 parts by mass of a chlorinated polyethylene.
On the other hand, instead of the methods of modifying the composition, a method for making the chloroprene rubber itself less staining was also proposed (see Patent Document 4). In the chloroprene rubber described in Patent Document 4, a metal salt of a disproportionate[ ] rosin acid having a sesquiterpene content of 0 to 1 mass % and a content ratio of (8,15-isopimaric acid)/(dihydropimaric acid) of 1 or more is used as the emulsifier, for prevention of the mold staining caused by the emulsifier component remaining in the chloroprene rubber.